.datignore equivalent

[paul90]

Support for ignoring files and directories has been lost during the move from dat to hyper.

While there is support retained in Beaker browser, though that no longer uses .datignore it does retain a memory of what was ignore in a previous sync. Maybe this just needs a cli command to allow interaction with the ignore list for a hyperdrive, and for that list to be respected when running sync/diff.

Also see hyperspace-org/hyperdrive-service#7, and hypercore-protocol/hyperdrive-daemon#53